The present invention relates to the field of HVAC systems and more particularly to the field of ventilation systems for buildings. The present invention specifically addresses demand-controlled ventilation (DCV) systems, in which the ventilation rate is determined based on actual occupancy levels in the ventilated zones, rather than default occupancy levels.
Both environmental and economic concerns in recent years have driven a move toward conserving energy by adjusting the rate of ventilation in various zones of a building to the actual demand for ventilation based on occupancy of the zone. ASHRAE ventilation standards now provide algorithms for adjusting ventilation rates based on occupancy in order to reduce energy consumption when demand falls below default levels. Systems have been developed that estimate occupancy based on levels of carbon dioxide measured in the ventilated space. But these CO2-based systems have several disadvantages, including the reliability and accuracy of the CO2 monitors and the costs associated with installing and maintaining them.
The present invention proposes an alternate method of determining the occupancy level of a ventilated space by monitoring ingress into and egress from the space. Active or passive identification tags incorporated in identification badges worn by building occupants are used to actually count the number of occupants of a given space, and that occupancy information is then relayed to a microprocessor-based control unit which applies the relevant ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) algorithm to compute the required ventilation rate. The control unit is interfaced with the building HVAC (heating, ventilating and air conditioning) system so as to adjust ventilation rates in each zone in accordance with the computed occupancy-based demand.
The prior art in this field includes some systems that use radio frequency identification (RFID) tags to monitor occupancy of a zone and others that use active RFID tags to set different parameters of an HVAC system directly, in accordance with the needs of the person or product to which the tag is attached. But none of the prior art systems has the capability of automatically adjusting ventilation rates based on detected occupancy levels.
The patent issued to Stortoni, U.S. Pat. No. 7,545,267, discloses a system in which RFID tags attached to climate-sensitive products signal a transponder in the storage area, which transponder signals one or more building control systems (such as HVAC) to adjust to the product's optimal environment. This system is not designed to address occupancy-based demand-controlled ventilation (DCV) and is not adaptable to that purpose. The Stortoni system requires expensive and bulky active RFID tags having substantial internal data content which serve no purpose in the DCV context.
The patent of Carrender, U.S. Pat. No. 6,927,687, discloses an apparatus that uses RFID tags and readers to monitor environmental conditions in a given area. The functions of this apparatus are unrelated to determining occupancy and/or controlling area ventilation rates.
The patent to Gazdzinski, U.S. Pat. No. 6,988,071, describes a “smart elevator” system that keeps track of occupancy levels in elevator car and/or destination floors by detecting RFID tags carried by passengers. While there is an embodiment of this system that involves control of HVAC in areas of the destination floor, this control is exercised by the elevator passenger manually activating a key pad or touch screen within the elevator. Therefore, the function of automatically setting ventilation levels in areas based on RFID-detected occupancy is not addressed.
The patent application of Agrawal, et al., US 2008/0048826, involves a system that uses an RFID badge to track an occupant's movement through an area and automatically disable certain hazards in the occupant's path for safety purposes. No means of counting occupants in the area or using that data to control ventilation rates is disclosed.
The patent issued to Myllymaki, U.S. Pat. No. 6,348,867, is a system that automates building control systems in accordance with an occupant's physiological condition as monitored by a wrist-held sensor. Occupancy-based DCV is not an object of this invention.
The patent of Funakoshi, et al., U.S. Pat. No. 5,156,203, discloses an air conditioning system that adjusts itself in response to preferred settings recorded on a “smart” ID card carried by the occupant. While automatic HVAC control is featured, it is not demand-controlled based on an occupancy count.
Consequently, the prior art discloses various “smart” tag systems that actively transmit internally stored data used directly for adjusting one or more HVAC settings. The prior art also discloses a system that uses passive tags to count occupants in a confined area. Combining these two types of systems is problematic, since the former require sophisticated active tags, while the latter uses simple passive tags. Even if they could be combined, however, the resulting system would still lack a means of compiling the occupancy data by ventilation zones and converting the compiled zonal data into ventilation control parameters.
The present invention bridges this gap in the prior art by providing a four-stage process by which tagged ID badges are detected in each room by a tag detector, and the tag IDs are wirelessly communicated to a zonal occupancy compiler. The zonal occupancy count arrived at by the compiler is wirelessly transmitted to a central DCV microprocessor, which interfaces with the ventilation controller of the building's HVAC system and sets the zonal ventilation rate based on the occupancy count and applicable ASHRAE standards.
The functional design of this process and the implementing apparatus will be outlined in the following section of this application, and then a more detailed description of two preferred embodiments of the invention will be presented, with the understanding that numerous alternate embodiments can be realized within the scope of the broad functional design.